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(No Model.)

D. DRAWBAUGH TELEPHONE TRANSMITTER.

5, i=2 VIEMMMV Patented Jan. 1, 1884.

ATTORN UNITED STATES PATENT QFFICE.

' DANIEL DRAWBAUGH, or EB'ERLYS MILL, PENNSYLVANIA.

TELEPHONE-TRANSMITTER.

srncrrrcn'rron formingpart of l'ietters Patent No. 291,472, datedJanuary l, 1884.

Application filed December 27, 1882. (No model.) Patented in EnglandSeptember 4,1883, No. 4,247, and in Belgii im September i To all whom itmay concern ing chamber is formed between said back board and the reardiaphragm, and also in the sound-reflector and the chamber therebyformed between the inner periphery of said reflector and the exterior ofthe inclosing-case, whereby sound-waves entering between the box and thereflector are reflected into the a space between the rear diaphragm andthe back board, and concentrated upon said diaphragm.

In the drawings, Figure l is a front view of the instrument with theouter diaphragm removed. The dotted lines show the lead of thecircuit-wires. Fig. 2 is a sectional view of the same on the line as m.Fig. 3 is a rear view of the frontdiaphragm.

Similar letters of reference indicate like parts.

A is the back board.

B is the box or case. i

D is the front diaphragm, of sheet metal. Said diaphragm sits in arecess in the case, as shown. In front of it is a ring, 0, of elasticmaterial, such as rubber.

E is the cover having a large central aperture, and secured in place byscrews or other suitable means. i The rear diaphragm, G, also of sheetmetal, is placed in an annular recess in the case, and in the rear of itis a rubber ring, H, and, finally, a wooden annular cover, I. Throughthe rear diaphragm, G, is made a circular opening, through which passesthe induction-coil J, which is secured to the baseboard A. Thearrangement of the low conductors is substantially the same as set forthin Letters Patent No. 266,615, granted to me October 31, 1882, and inother applications of mine now pending.

K and L are pieces of carbon, shaped as shown, and held in metalbrackets M and N, which brackets are secured to the inner sides of thediaphragms G and D. The pieces K and L do not meet. Upon their proximateinclined sides rests a cylindrical carbon, 0. Above this carbon, andserving to keep it in place when the instrument is inverted, is a bar,1?, secured to the interiorof the case, as shown in Fig. 1.

Between the annular rear cover, I, and the back board A are studs Q,which support the case B at a distance from the back board.

Surrounding the case B, and attached to the back board A, is an annularsound-reflector, R, having an inclined inner periphery, so thatsound-waves entering the chamber between said reflector and the outerperiphery of the cylindrical case B are reflected or concen. trated intothe space or chamber between the back board A and the rear diaphragm, G,and are thus enabled to act and be in some measure concentrated upon thelatter. way both diaphragms of the instrument may be affectedsimultaneously-the front diaphragm, D, by sound-waves directly impingingupon it, and the rear diaphragm, G, by waves reflected and concentratedinto the space between it and the back board. This results incompression being applied to the series of carbons from both ends ofsaid series, which renders the apparatus more sensitive in itsoperation.

The circuits in the instrument lead as follows: from one pole of thebattery to the binding-post 1; by wire a (dotted lines) to the primaryof the induction-coil J; by wire I) to the carbon K; thence to carbon 0,carbon L, and diaphragm D, on the latter to contact-piece F; to springcontact-piece T, when said contact pieces S and T are in contact; to thewire 0 (dotted lines) and binding-post 2, and then to the other pole ofthe battery.

U is a post on which a receiving-telephone may be hung when out of use,the ring on said telephone pushing upward the contact-piece T, and thusbreaking the circuit. The post U is shown only in Fig. 1.

The secondary wire of the induction-coil J In this Q serum:

connects with the binding-posts 3 and 4 by wires d d, (dotted lines,)which posts communicate with the line.

Branch wires 6 e (dotted lines) from the wires (1 d connect withbinding-posts 5 and 6, to which posts the receiving-telephone isattached. g

I claim as my invention 1. In a telephone, the combination of twodiaphragms covering opposite sides of the inclosing box or case of theinstrument and rigidly secured to said box or case, a means of modifyingan electric current so as to render it capable of transmittingarticulate speech, arranged between said diaphragms and influenced bythe vibrations of both of them, and a means of reflecting orconcentrating sound waves upon that one of the two diaphragms which doesnot face the source of sound, substantially as described.

2. In a telephone, in combination with an inolosing box or casecontaining two diaphragms on opposite sides thereof, and a means ofmodifying an electric current so asto render it capable of transmittingarticulate speech, arranged between said diaphragms and influenced bythe vibrations of both of them, two communicating sound -'receivingchambers one chamber being formed annularly, or substantially so, aroundthe exterior of the inclosing-case, and the other being formed in rearof said case, substantially as described.

3. The combination of, first, a telephone containing an inclosing-case,two diaphragms, and means for modifying an electric current so as torender it capable of transmitting articulate speech; second, a backboard or base, third, supports arranged between the rear side of saidtelephone and the back board; and,fourth, a sound-reflecting projectionattached to said back board and surrounding the telephonecase,substantially as described.

DANIEL DRAWBAUGH.

Witnesses:

WILLIAM C. SToEvER, M. W. JACOBS.

